1. Field of the Invention
The present invention relates to a magnetic sensor, and in particular to a magnetic sensor with a bridge circuit including magnetoresistance effect elements.
2. Description of the Related Art
In recent years, magnetic sensors have been used to detect the rotation angle of a rotator such as a steering wheel in a vehicle.
For example, JP 8-226960 discloses a magnetic sensor with a bridge circuit including magnetoresistance effect elements (MR elements), the bridge circuit being configured to provide an output that changes in accordance with the direction of an external magnetic field. In such a magnetic sensor, a magnet or the like is installed on the rotator, so that the direction of the external magnetic field changes in accordance with rotation of the rotator. The rotation angle of the rotator is detected by detecting the direction of the external magnetic field. Thus, naturally, highly accurate detection of the direction of the external magnetic field is required. For this purpose, much effort has been made to more accurately measure the output voltage from the bridge circuit including MR elements.
For example, JP 2009-115688 discloses a magnetic sensor with a bridge circuit including four MR elements and an amplifying circuit connected to the bridge circuit, the amplifying circuit including a feedback resistor for setting a gain having an opposite temperature characteristic to that of the bridge circuit. In such a magnetic sensor, a change in output voltage due to temperature change is suppressed by the feedback resistor for setting a gain having an opposite temperature characteristic to that of the bridge circuit. Consequently, a change in sensitivity of the magnetic sensor due to temperature change is compensated for, and thus the detection accuracy of the magnetic sensor is improved.
However, the above-described measure fails to take into account a shunt current flowing from the bridge circuit of the magnetic sensor into the external device (amplifying circuit) during measurement of the output voltage. The shunt current causes an electrical unbalance of the bridge circuit, resulting in an error in the measured value of the output voltage itself.